Tokyo: Japan marks on Friday the 20th anniversary of a nerve gas attack in the Tokyo subway by an apocalyptic cult that killed 13 and injured more than 6,000 people.

Members of the Aum Supreme Truth cult released Nazi-developed sarin in five subway trains during co-ordinated rush-hour attacks on March 20, 1995.

Thirteen Aum members, including its leader Shoko Asahara, are on death row after being convicted over the subway attack. The murder trial of the final suspect, Katsuya Takahashi, began in January after his arrest in 2012.

Among the events planned for Friday`s anniversary, staff at the central Kasumigaseki metro station will hold a moment of silence at 8:00 am (2300 GMT) to remember two former colleagues who died in the attack.

Five cult members dumped packages of sarin on busy trains during rush-hour, puncturing them with sharpened umbrella tips, before being driven away from a pre-determined station by their co-conspirators.

The sarin -- a nerve gas so toxic that a single drop can kill a person -- evaporated as thousands of unwitting commuters got on and off each train.

Staff and passengers were among the dead. Many of those sickened only realised what had happened as their symptoms worsened throughout the day and news broadcasts began piecing events together.

Two decades later, Japan remains largely baffled by why the cultists -- including scientists and doctors who had graduated from the country`s top universities -- launched the attack.

Near-blind yoga master Asahara, now 60, preached a blend of Buddhist and Hindu dogma sprinkled with visions of the apocalypse and attracted some 10,000 followers at the height of his popularity.

He developed an obsession with the Nazi-developed sarin gas, and became paranoid that his enemies would use it to kill him.

Prosecutors say the attack was launched because the cult wanted to disrupt attempts by the police to crack down on the group and to throw Tokyo into chaos in order to realise Asahara`s dream of an apocalyptic war.